1. Field of the Invention
The present invention relates to a flexible tube assembly for an endoscope, which constitutes a body of an insertion portion of the endoscope.
2. Description of the Related Art
A typical endoscope is disclosed in, e.g., Japanese Utility Model Disclosure Nos. 59-190201 and 60-187701. This endoscope comprises operation and insertion sections. An angle knob for operating a bending portion of the insertion section, an eyepiece for observation, and other operation means are mounted on the operation section.
A body of the insertion section is constituted by a flexible tube assembly. Light and image guides, a forceps channel tube, and the like are stored in the flexible tube assembly. An operator can observe a portion in front of the distal end of the insertion section through the image guide connected to the eyepiece.
The bending portion arranged on the distal end of the insertion section can be bent in a desired direction upon operation of the angle knob. For this reason, the operator can observe a desired portion in a body cavity using this endoscope.
A helical tube is arranged at an innermost portion of the flexible tube assembly so as to prevent the flexible tube assembly from being collapsed by an external force. This helical tube is constituted by a belt-like plate coiled in a helical shape with gaps. A net tube covers the outer surface of the helical tube to prevent its twisting. In addition, the outer surface of the net tube is covered with an outer sheath formed of a thermoplastic elastomer.
When the insertion section of the endoscope having the above-described arrangement is inserted into a body cavity, the insertion section is bent in accordance with the shape of the body cavity. In this case, a side wall of a curvature center side of the bent flexible tube assembly is contracted, whereas a side wall on the opposite side is expanded. At the same time, gaps are reduced on the curvature center side and are widened on the opposite side.
When the insertion portion of the endoscope is inserted into, e.g., the duodenum of a patient, it is bent at a relatively small radius of curvature. For this reason, especially in such a case, a flexible tube assembly which can be bent at a small radius of curvature is required.
When an insertion section of an endoscope having a typical flexible tube assembly is inserted into, e.g., the duodenum of a patient, before the insertion section is bent along the shape of the duodenum, gaps on one side of a helical tube disappear and hence the insertion section cannot be sufficiently bent. This may cause a pain to the patient, or distort the helical tube and damage image and light guides, and the like stored therein. Furthermore, the overall flexible tube assembly may be disabled.
If the gaps of the helical tube are excessively expanded in order to solve such a problem, a net tube may be pinched in the gaps and damaged.